System for a towing vehicle

ABSTRACT

The present invention relates to a vehicle control system (1) for controlling a trailer (5) coupled to a vehicle (3) during a reversing operation. The vehicle control system includes a processor (29) configured to determine an actual trailer travel direction (TACT) based on one or more sensor signals. The processor (29) receives a demanded trailer travel direction (TDEM), for example from a user. A maximum permissible hitch angle (ϕMAX) is calculated by the processor (29) and the demanded trailer travel direction (TDEM) is limited to an angle less than or equal to the calculated maximum permissible hitch angle (ϕMAX). The present invention also relates to a vehicle (3) incorporating the vehicle control system (1); and a method of controlling the reversing of the trailer (5).

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/784,220, filed Oct. 13, 2015, which itself is a 35 U.S.C. § 371national stage application of PCT Application No. PCT/EP2014/058387,filed on Apr. 24, 2014, which claims priority from Great Britain PatentApplication No. 1307524.7, filed on Apr. 26, 2013, the contents of whichare incorporated herein by reference in their entireties. Theabove-referenced PCT International Application was published in theEnglish language as International Publication No. WO 2014/174037 A1 onOct. 30, 2014.

TECHNICAL FIELD

The present invention relates to a system for a towing vehicle; a humanmachine interface (HMI); a method of controlling a trailer coupled to avehicle during a reversing operation; and a vehicle.

BACKGROUND OF THE INVENTION

It is known from GB 2447672 to provide a computing unit to calculate ahitch angle between a trailer and a vehicle. The computing unit usesimage data from three video cameras, fitted respectively to the rear ofthe vehicle and one on each door mirror, to track the position of atrailer-mounted marker to determine the position of the trailer relativeto the vehicle. The computing unit can also predict a trailer path andthis is output to the driver on a display as guide lines overlaid onto acamera view.

At least in certain embodiments, the present invention aims to providean improved system.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a system; a human machineinterface (HMI); a method of controlling a trailer coupled to a vehicleduring a reversing operation; and a vehicle.

According to a further aspect of the present invention there is provideda vehicle control system for reversing a trailer coupled to a vehicle,the vehicle control system comprising a processor configured to:

-   -   determine an actual trailer travel direction based on one or        more sensor signals;    -   receive a demanded trailer travel direction; and    -   calculate a maximum permissible hitch angle;    -   wherein the processor is configured to limit the demanded        trailer travel direction to an angle less than or equal to the        calculated maximum permissible hitch angle. The demanded trailer        travel direction represents a target trailer travel direction        and is typically user-generated. By limiting the range of        trailer travel direction that can be demanded by the user, the        vehicle control system can prevent the user from demanding a        trailer travel direction which exceeds the maximum permissible        hitch angle. In use, the control system can prevent the actual        trailer travel direction increasing above the maximum        permissible hitch angle.

The maximum permissible hitch angle typically corresponds to or is basedon a jack-knife angle of the trailer. The jack-knife angle is the angleabove which the hitch angle cannot be reduced by reversing the vehicle.The vehicle control system can help to avoid the trailer jack-knifingwhile it is being reversed. The processor can be configured to output amaximum hitch angle signal based on the calculated angle. The maximumpermissible hitch angle could be smaller than the jack-knife angle ofthe trailer to introduce an error margin. The maximum permissible hitchangle could be defined as the jack-knife angle of the trailer less apre-defined angular offset. The pre-defined angular offset could be 1°,2°, 5° or 10°, for example. Alternatively, the maximum permissible hitchangle could be a function of the jack-knife angle of the trailer, forexample substantially equal to 95%, 97% or 99% of the calculatedjack-knife angle.

The processor can be configured to estimate a distance to be travelledby the vehicle at least substantially to match the actual trailer traveldirection with the demanded trailer travel direction. This aspect of thepresent invention is believed to be patentable independently.

According to a further aspect of the present invention there is provideda vehicle control system for reversing a trailer coupled to a vehicle,the vehicle control system comprising a processor configured to:

-   -   determine an actual trailer travel direction based on one or        more sensor signals;    -   receive a demanded trailer travel direction; and    -   estimate a distance to be travelled by the vehicle at least        substantially to match the actual trailer travel direction with        the demanded trailer travel direction. The processor can predict        the convergence of the actual trailer travel direction and the        demanded trailer travel direction. The processor can be        configured to output a distance signal based on the estimated        distance to be travelled.

The processor can be configured to calculate a maximum permissible hitchangle. The processor can optionally also be configured to limit thedemanded trailer travel direction to an angle less than or equal to saidmaximum permissible hitch angle.

The system can comprise a display operative to display systeminformation based on the output(s) from said processor. The display canbe in communication with said processor. The system information can bedisplayed as an overlay on a video image, for example a video image fromone or more reversing cameras. The display can be operative to displayone or more of the following:

-   -   (a) the actual trailer travel direction;    -   (b) the demanded trailer travel direction;    -   (c) a numerical or graphical indication of the estimated        distance to be travelled;    -   (d) a location where the actual trailer travel direction will at        least substantially match the demanded trailer travel direction.    -   (e) an angular offset between said actual trailer travel        direction and said demanded trailer travel direction;    -   (f) the maximum permissible hitch angle;    -   (g) a current steering angle; and    -   (h) one or more trajectory lines representing a predicted path        of the vehicle and/or the trailer.

The actual trailer travel direction can be indicated by a first arrow.The first arrow could be a vector arranged to display both the directionof trailer travel and also the velocity (magnitude) of the trailertravel. The demanded trailer travel direction can be indicated by asecond arrow. The first arrow and the second arrow can extend radiallyfrom a common origin, for example positioned along a centre line of thevehicle. The origin can be overlaid onto the video image to coincidewith the position of the tow bar of the vehicle.

The current hitch angle could be displayed. The angular velocity(degrees/second) at which the hitch angle is changing could also bedisplayed, for example as a (positive/negative) numerical value and/or agraphical symbol, such as an arrow, representing direction (clockwise orcounter-clockwise) and/or magnitude. The maximum permissible hitch anglecan be displayed as a marker, such as a continuous line or a dashedline. The maximum permissible hitch angle can be displayed for bothclockwise and counter-clockwise directions.

The trajectory line(s) can represent a predicted path of the vehicleand/or the trailer. For example, a pair of parallel trajectory lines canbe displayed to represent the path followed by the wheels of the vehicleand/or the trailer. The location where the actual trailer traveldirection will at least substantially match the demanded trailer traveldirection could be displayed by a marker or symbol on said trajectoryline(s).

A steering angle of the vehicle could be controlled manually. Theestimated distance could, for example, be calculated based on a currentsteering angle selected by the user. The user could optionally determinethe optimum steering angle by rotating the steering wheel to identifythe minimum estimated distance. The control system could be configuredto output prompts to the user to control the steering angle, for exampleto request that the driver increases or decreases the steering angle.

Alternatively, the steering angle can be controlled automatically. Theprocessor can be configured to output a steering control signal tocontrol a steering angle of the vehicle. The steering control signal canbe output to an electronic power assisted steering (EPAS) module. Theangular velocity of changes in the vehicle steering angle(degrees/second) can be adjusted in proportion to the vehicle speed. Thevehicle speed can be controlled automatically, for example as a furtherfunction of the processor. Alternatively, the vehicle speed can becontrolled by the driver, for example by providing acceleration andbraking inputs using the vehicle controls. When the vehicle controlsystem is operating to match the actual and demanded trailer traveldirections, the processor can be configured to limit the speed of thevehicle and/or to limit the acceleration of the vehicle.

The processor can be configured to calculate a rate of convergence ofthe actual trailer travel direction and said demanded trailer traveldirection. The display system can be operative to display the rate ofconvergence. The rate of convergence could be displayed as a numericalrepresentation and/or a graphical representation.

The image system can comprise one or more optical cameras disposed onsaid vehicle and/or said trailer. The processor can be configured toreceive proximity data from other sensors, for example ultrasonicsensors or radar disposed on the vehicle and/or the trailer.

The demanded trailer travel direction can be specified by a user. Thedemanded trailer travel direction could be specified using the steeringwheel of the vehicle; or an input device other than the steering wheel.For example, the input device can comprise an input for an on-boardinformation/entertainment (infotainment) system. The input device cancomprise a rotary knob, a jog switch/wheel, a touchscreen, a touchpanel, a joystick or the like. In alternate embodiments, the demandedtrailer travel direction could be set using the vehicle steering wheel.

The system can be implemented as a component of a human machineinterface (HMI). The display and/or the input device can form part ofthe HMI. According to a still further aspect of the present invention,there is provided a HMI comprising a vehicle control system as describedherein. The HMI can be configured to inhibit or prevent selection of ademanded trailer travel direction exceeding the calculated maximumpermissible hitch angle.

According to a further aspect of the present invention there is provideda system for reversing a trailer coupled to a vehicle, the vehiclecontrol system comprising a processor and a display system, theprocessor being configured to:

-   -   determine an actual trailer travel direction based on one or        more sensor signals; and    -   receive a demanded trailer travel direction;    -   wherein the display system is operative simultaneously to        display the actual trailer travel direction and the demanded        trailer travel direction. The processor can also be configured        to calculate a maximum permissible hitch angle. The display        system can be operative to display the maximum permissible hitch        angle at the same time as the actual and demanded trailer travel        directions. The maximum permissible hitch angle can correspond        to or be based on the jack-knife angle of the trailer.

According to a still further aspect of the present invention there isprovided a method of controlling a trailer coupled to a vehicle during areversing operation, the method comprising:

-   -   determining an actual trailer travel direction based on one or        more sensor signals;    -   receiving a demanded trailer travel direction; and    -   calculating a maximum permissible hitch angle;    -   wherein the method comprises limiting the demanded trailer        travel direction to an angle less than or equal to the        calculated maximum permissible hitch angle. The method can        comprise displaying the maximum permissible hitch angle on a        display. The maximum permissible hitch angle can be overlaid        onto a video image, for example from a rearward facing camera.        The method can comprise displaying the demanded trailer travel        direction and/or the actual trailer travel direction on said        display.

According to a yet further aspect of the present invention there isprovided a method of controlling a trailer coupled to a vehicle during areversing operation, the method comprising:

-   -   determining an actual trailer travel direction based on one or        more sensor signals;    -   receiving a demanded trailer travel direction; and    -   estimating a distance to be travelled by the vehicle at least        substantially to match the actual trailer travel direction with        the demanded trailer travel direction.

The methods described herein can each be computer-implemented, forexample on a computational apparatus comprising one or moremicroprocessors. According to a yet further aspect of the presentinvention there is provided a computer program product comprising acomputer readable storage medium including computer readable programcode, where the computer readable program code when executed on acomputer causes the computer to perform the method(s) described herein.

The term processor used herein is to be understood as covering bothsingle processors and multiple processors.

Within the scope of this application it is expressly intended that thevarious aspects, embodiments, examples and alternatives set out in thepreceding paragraphs, in the claims and/or in the following descriptionand drawings, and in particular the individual features thereof, may betaken independently or in any combination. Features described inconnection with one embodiment are applicable to all embodiments, unlesssuch features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described, by way ofexample only, with reference to the accompanying figures, in which:

FIG. 1 shows a plan view of a trailer coupled to a vehicle incorporatinga system in accordance with an embodiment of the present invention;

FIG. 2 shows a schematic representation of the vehicle and the system inaccordance with an embodiment of the present invention;

FIG. 3 illustrates the vehicle and trailer dimensions and associatednomenclature;

FIG. 4 shows a first display image from a rear camera mounted to thevehicle with information overlaid onto the video image to facilitatereversing the trailer (which is omitted from the image for clarity); and

FIG. 5 shows a second display image from the rear camera with analternate set of information overlaid onto the video image.

DETAILED DESCRIPTION OF AN EMBODIMENT

A system 1 for assisting with the reversing of a vehicle 3 and a trailer5 in accordance with an embodiment of the present invention will now bedescribed with reference to FIGS. 1 to 4.

The system is operable to facilitate reversing of the trailer 5 when itis coupled to the vehicle 3 (the combination of the vehicle 3 and thetrailer 5 can be referred to as ‘a rig’). More specifically, the system1 is configured to control the steering of the vehicle 3 such that thetrailer 5 is reversed in a direction specified by the user. In thepresent embodiment, the operation of the throttle and brakes of thevehicle 3 are controlled by the user.

A plan view of the vehicle 3 and the trailer 5 are shown in FIG. 1. Thevehicle 3 has four wheels W1-4 and the front wheels W1, W2 of thevehicle 3 are steerable in conventional manner. The trailer 5 has twowheels TW1, TW2 having a fixed orientation.

As shown in FIG. 2, the vehicle 3 is provided with an imaging systemcomprising a centrally mounted rear camera 9; and left and right sidecameras 10, 11 mounted in respective wing mirrors 13, 15. The cameras 9,10, 11 are optical cameras arranged to face to the rear of the vehicle 3and their fields of view V1, V2, V3 are illustrated by dashed trianglesin FIG. 1. The vehicle 3 optionally also comprises an obstructiondetection system, for example side radar systems for detecting thepresence of obstructions in the rear three quarters position of thevehicle 3.

A tow hitch 17 is mounted to the vehicle 3 for coupling to a trailercoupling 19 mounted to the trailer 5. The tow hitch 17 is an upwardlyprojecting tow ball in the present embodiment. The trailer coupling 19is mounted to a hitch frame 21 disposed at the front of the trailer 5.In the present embodiment, the hitch frame 21 is an A-frame having afront apex 23 to which the trailer coupling 7 is mounted. A target 25 ismounted to a front face 27 of the trailer 5 to enable the position ofthe trailer 5 relative to the vehicle 3 to be determined, as describedherein. The target 25 is a visible image comprising three circlesarranged in a triangular formation. It will be appreciated that thepresent invention can be implemented with other targets 25, for examplecomprising different symbols/images or non-visible targets.

The system 1 comprises an electronic control unit (ECU) having anelectronic processor 29. The processor 29 comprises image processingmeans in the form of an image processing module 29A for analysing theimage data. The cameras 9, 10, 11 each output image data to the imageprocessing module 29A for analysis. In use, the image processing module29A analyses the image data to identify feature sets corresponding topredefined features. In the present embodiment, the target 25 defines afirst feature set 31 and the hitch frame 21 defines a second feature set33. The image processing module 29A identifies the first feature set 31and/or the second feature set 33 within the image data to determine theposition and orientation of the trailer 5 in relation to the vehicle 3.

The first feature set 31 can be defined in a target geometry file; andthe second feature set 33 can be defined in a trailer geometry file. Thegeometry files can both be stored on a storage medium accessible to theprocessor 29. The target geometry file can be predefined, for example todefine a specific target design supplied by the vehicle manufacturer.The trailer geometry file can comprise data defining the geometry of thehitch frame 21 and optionally also the length and/or wheelbase of thetrailer 5. A plurality of trailer geometry files can be stored, forexample to represent different sizes/configurations of trailers 5. Thesystem 1 can allow a user to select a predefined trailer model or todefine a custom trailer model.

The processor 29 further comprises vehicle/trailer guidance means in theform of a guidance module 29B. The guidance module 29B is provided toassist with guiding the trailer 5 when the vehicle 3 and the trailer 5are being reversed together. In particular, the guidance module 29B isconfigured to control a steering angle θ of the front wheels W1, W2 ofthe vehicle 3 to guide the trailer 5 in a demanded trailer traveldirection T_(DEM). As described herein, the demanded travel directionT_(DEM) is defined by the user and represents a target direction oftravel for the trailer 5.

The vehicle 3 has a first longitudinal axis X1 and the trailer 5 has asecond longitudinal axis X2. The angular offset between the first andsecond longitudinal axes X1, X2 is referred to as the hitch angle ϕ.During reversing, the trailer 5 travels in a direction T_(ACT)corresponding to the hitch angle ϕ (unless the hitch angle ϕ exceeds ajack-knife angle for the trailer 5, as described herein).

The image processing module 29A calculates the hitch angle ϕ, withreference to said first feature set 31 and/or said second feature set33, and outputs a hitch angle signal to the guidance module 29B. Whenreversing, the guidance module 29B calculates the required steeringangle 9 based on the following equation:θ_(t+1)=θ_(t)+min(max(k(ϕ_(req)−ϕ_(cur)),−α),α)

-   Where: θ_(t+1) and θ_(t) are the steering angles of the vehicle 3 at    frame t+1 and t (auto steering command from the algorithm and    current steering from the CAN respectively);    -   ϕ_(req) and ϕ_(cur) are the requested and current hitch angles;    -   α is the maximum steering offset value; and    -   k is a constant multiplier.

The value of the gain k can be calculated based on the relationshipbetween θ and ϕ, as shown in FIG. 3. When the trailer hitch length Lplus the towbar offset of the vehicle h is equal to the vehiclewheelbase d, then the relationship between θ and ϕ is one (1) for smallangles and so the gain k can be set to a value of one (1). The gain kcan therefore be calculated based on the following equation:

$k = \frac{L + h}{d}$

-   Where: L is the hitch length of the trailer 5;    -   h is the tow bar offset of the vehicle 3;    -   d is the wheelbase of the vehicle 3;

The gain k thereby compensates for the fact that longer trailers takelonger to reach the requested hitch angle ϕ.

The guidance module 29B is configured to calculate a maximum permissiblehitch angle ϕ_(MAX). If the hitch angle ϕ exceeds the maximumpermissible hitch angle ϕ_(MAX) (which in the present embodiment is thejack-knife angle of the trailer 5), it is no longer possible to reducethe hitch angle ϕ by continuing to reverse (i.e. the trailer 5 hasjack-knifed). With reference to FIG. 3, the guidance module 29Bcalculates the maximum permissible hitch angle ϕ_(MAX) by applying thefollowing set of equations:

$R = \frac{d}{\tan(\theta)}$$\phi = {{\cos^{- 1}\left( \frac{{- {Lh}} + {R\sqrt{R^{2} + h^{2} - L^{2}}}}{R^{2} + h^{2}} \right)}\mspace{14mu}{for}\mspace{14mu}{positive}\mspace{14mu}\theta}$$\phi = {{- {\cos^{- 1}\left( \frac{{- {Lh}} - {R\sqrt{R^{2} + h^{2} - L^{2}}}}{R^{2} + h^{2}} \right)}}\mspace{14mu}{for}\mspace{14mu}{negative}\mspace{14mu}\theta}$

-   Where: R is the turning radius;    -   θ is the steering angle of the vehicle 3;    -   d is the wheelbase of the vehicle 3;    -   h is the tow bar offset of the vehicle 3;    -   L is the hitch length of the trailer 5;

The wheelbase d, the tow bar offset h and the maximum steering angleθ_(MAX) of the vehicle 3 are defined for the vehicle 3. The hitch lengthL of the trailer 5 is entered during trailer setup by the user (or canbe determined during a calibration exercise). The guidance module 29Boutputs a maximum hitch angle signal to indicate the maximum permissiblehitch angle ϕ_(MAX) for the current steering angle θ. The guidancemodule 29B is configured to inhibit the selection of a demanded trailertravel direction T_(DEM) which is greater than the maximum permissiblehitch angle ϕ_(MAX).

The guidance module 29B is configured to calculate the distance to betravelled by the vehicle 3 before the actual trailer travel directionmatches the demanded trailer travel direction T_(DEM). The distance iscalculated based on a predictive path algorithm which models the path tobe followed by the vehicle 3. The guidance module 29B calculates theinitial required steering angle θ to achieve the desired hitch angle ϕ,then iteratively calculates the required steering angle θ and hitchangle ϕ. The distances to be travelled by the vehicle 3 between each ofthe iterations are then summed to provide the total distance to betravelled. The guidance module 29B outputs a distance signal to indicatethe distance to be travelled by the vehicle 3.

In use, the guidance module 29B is configured to output a steeringcontrol signal operative to control the steering angle θ of the frontwheels W1, W2 to adjust the hitch angle ϕ, thereby modifying the actualtrailer travel direction. Specifically, the guidance module 29B adjuststhe steering angle θ (which can be positive or negative in relation to areference point) to increase or decrease the hitch angle ϕ. The actualtrailer travel direction T_(ACT) can thereby be matched to the demandedtrailer travel direction T_(DEM) specified by the user. The hitch anglesignal is updated at least substantially in real time and the guidancemodule 29B makes corresponding real time adjustments to the steeringcontrol signal. The guidance module 29B controls the hitch angle ϕ sothat the difference between T_(ACT) and T_(DEM) is at leastsubstantially zero. A tolerance of +/−0.5° between T_(ACT) and T_(DEM)provides a good result.

The guidance module 29B can generate a control sequence to reduce orminimise the distance travelled by the vehicle 3 and the trailer 5 toachieve the demanded trailer travel direction T_(DEM).

The steering angle control signal is output to an electronic powerassisted steering (EPAS) module 35 to control the angle of a steeringwheel 37 to provide a required steering angle θ for the front wheels W1,W2. The EPAS module 35 automatically adjusts the angular orientation ofthe steering wheel 37 to provide the appropriate steering angle θ at thefront wheels W1, W2 to control the vehicle 3 to match the actual trailertravel direction T_(ACT) with the demanded trailer travel directionT_(DEM).

The system 1 comprises a human machine interface (HMI) module 39. TheHMI module 39 is coupled to a display screen 41 which displays a videoimage 43 from the rear camera 9 (or a composite image derived from theimage data for each of the cameras 9, 10, 11). As shown in FIG. 4, theHMI module 39 is configured to overlay graphical symbols over the videoimage 43. In the present embodiment, the HMI module 39 displays a firstarrow A to indicate the actual trailer travel direction T_(ACT); and asecond arrow B to indicate the demanded trailer travel directionT_(DEM). The user can adjust the demanded trailer travel directionT_(DEM) by varying the orientation of the second arrow B using an inputdevice in communication with the HMI module 39. In the presentembodiment, the input device is a rotary knob forming part of thevehicle infotainment system.

In addition to displaying the first and second arrows A, B, the HMImodule 39 receives the maximum hitch angle signal from the guidancemodule 29B. The HMI module 39 displays the maximum permissible hitchangle ϕ_(MAX) on the display screen 41 as an overlay of the video image43 from the rear camera 9. As illustrated in FIG. 4, the maximumpermissible hitch angle ϕ_(MAX) in clockwise (+ve) and counter-clockwise(−ve) directions are displayed as first and second dashed lines 45 a, 45b. The guidance module 29B inhibits selection of a demanded trailertravel direction T_(DEM) which is greater than the maximum permissiblehitch angle ϕ_(MAX). This restriction on the demanded trailer traveldirection T_(DEM) is applied by the HMI module 39 which prevents thesecond arrow B being oriented at an angle greater than the maximumpermissible hitch angle ϕ_(MAX).

The guidance module 29B outputs the steering angle control signal to theHMI module 39 and the current steering angle θ is represented by asteering wheel symbol 47 which representing the steering wheel 37. Theangular orientation of the steering wheel symbol 47 provides anapproximate representation of the angular orientation of the steeringwheel 37. A numerical indication of the steering angle could bedisplayed instead of, or in addition to, the steering wheel symbol 47.

The HMI module 39 is configured to overlay a predicted vehicletrajectory onto the video image 43. As shown in FIG. 5, the HMI module39 displays a first pair of parallel lines 49 representing the predictedtrajectory of the vehicle 3; and a second pair or parallel lines 51representing the predicted trajectory of the trailer 5.

The present invention is applicable to a range of different types oftrailer 5. For example, the trailer 5 can be a caravan, a goods trailer,a flatbed trailer, a van trailer, a livestock trailer and so on.Similarly, the present invention is applicable to a range of differenttypes of vehicles 3. For example, the vehicle 3 can be a motor vehicle,such as an off-road or sports utility vehicle; or a towing engine ortractor for a semi-trailer truck.

It will be appreciated that various changes and modifications can bemade to the system 1 described herein without departing from the presentinvention. Further aspects of the present invention are set out in thefollowing numbered paragraphs:

1. A vehicle control system for reversing a trailer coupled to avehicle, the vehicle control system comprising a processor configuredto:

-   -   determine an actual trailer travel direction based on one or        more sensor signals;    -   receive a demanded trailer travel direction; and    -   calculate a maximum permissible hitch angle;    -   wherein the processor is configured to limit the demanded        trailer travel direction to an angle less than or equal to the        calculated maximum permissible hitch angle.        2. A vehicle control system as described in paragraph 1, wherein        the processor is configured to estimate a distance to be        travelled by the vehicle at least substantially to match the        actual trailer travel direction with the demanded trailer travel        direction.        3. A vehicle control system for reversing a trailer coupled to a        vehicle, the vehicle control system comprising a processor        configured to:    -   determine an actual trailer travel direction based on one or        more sensor signals;    -   receive a demanded trailer travel direction; and    -   estimate a distance to be travelled by the vehicle at least        substantially to match the actual trailer travel direction with        the demanded trailer travel direction.        4. A vehicle control system as described in paragraph 3, wherein        the processor is configured to calculate a maximum permissible        hitch angle; and, optionally, also to limit the demanded trailer        travel direction to an angle less than or equal to said maximum        permissible hitch angle.        5. A vehicle control system as described in paragraph 1 further        comprising a display in communication with said processor and        operative to display system information for a driver.        6. A vehicle control system as described in paragraph 5, wherein        the display is operative to display one or more of the        following:    -   (a) the actual trailer travel direction;    -   (b) the demanded trailer travel direction;    -   (c) a numerical or graphical indication of the estimated        distance to be travelled;    -   (d) a location where the actual trailer travel direction will at        least substantially match the demanded trailer travel direction.    -   (e) an angular offset between said actual trailer travel        direction and said demanded trailer travel direction;    -   (f) the maximum permissible hitch angle;    -   (g) a current steering angle;    -   (h) one or more trajectory lines representing a predicted path        of the vehicle and/or the trailer.        7. A vehicle control system as described in paragraph 1, wherein        the processor is configured to output a steering control signal        to control a steering angle of the vehicle.        8. A vehicle control system as described in paragraph 7, wherein        the processor is configured to output the steering control        signal to an electronic power assisted steering (EPAS) module.        9. A vehicle control system as described in paragraph 1, wherein        the demanded trailer travel direction is specified by a user.        10. A vehicle comprising a vehicle control system as described        in paragraph 1.        11. A method of controlling a trailer coupled to a vehicle        during a reversing operation, the method comprising:    -   determining an actual trailer travel direction based on one or        more sensor signals;    -   receiving a demanded trailer travel direction; and    -   calculating a maximum permissible hitch angle;    -   wherein the method comprises limiting the demanded trailer        travel direction to an angle less than or equal to the        calculated maximum permissible hitch angle.        12. A method as described in paragraph 11 comprising outputting        a steering control signal to control a steering angle of the        vehicle.        13. A method as described in paragraph 12, wherein the steering        control signal is output to an electronic power assisted        steering (EPAS) module to provide automated control of the        steering angle of the vehicle.        14. A method of controlling a trailer coupled to a vehicle        during a reversing operation, the method comprising:    -   determining an actual trailer travel direction based on one or        more sensor signals;    -   receiving a demanded trailer travel direction; and    -   estimating a distance to be travelled by the vehicle at least        substantially to match the actual trailer travel direction with        the demanded trailer travel direction.        15. A method as described in paragraph 14 comprising displaying        a numerical or graphical indication of the estimated distance to        be travelled by the vehicle.

The invention claimed is:
 1. A system for a vehicle having a trailercoupled thereto, the system comprising a processor configured to:receive a demanded trailer travel direction; calculate a maximumpermissible hitch angle; limit the demanded trailer travel direction toan angle less than or equal to the calculated maximum permissible hitchangle; and responsive to calculating the maximum permissible hitchangle, output a steering control signal to control a steering angle ofthe vehicle to guide the trailer in the demanded trailer traveldirection.
 2. The system as claimed in claim 1, wherein the processor isfurther configured to determine an actual trailer travel direction basedon one or more sensor signals, and to estimate a distance to betravelled by the vehicle at least substantially to match the actualtrailer travel direction with the demanded trailer travel direction. 3.The system as claimed in claim 1, further comprising a display incommunication with the processor and operative to display systeminformation for a driver.
 4. The system as claimed in claim 3, whereinthe display is operative to display one or more of the following: (a)the actual trailer travel direction; (b) the demanded trailer traveldirection; (c) a numerical or graphical indication of the estimateddistance to be travelled; (d) a location where the actual trailer traveldirection will at least substantially match the demanded trailer traveldirection; (e) an angular offset between the actual trailer traveldirection and the demanded trailer travel direction; (f) the maximumpermissible hitch angle; (g) a current steering angle; and (h) one ormore trajectory lines representing a predicted path of the vehicleand/or the trailer.
 5. The system as claimed in claim 1, wherein theprocessor is further configured to output the steering control signal toan electronic power assisted steering (EPAS) module.
 6. The system asclaimed in claim 1, wherein the demanded trailer travel direction isspecified by a user.
 7. A vehicle comprising the system as claimed inclaim
 1. 8. A method of operating a vehicle coupled to a trailer duringa reversing operation, the method comprising: receiving a demandedtrailer travel direction; calculating a maximum permissible hitch angle;limiting the demanded trailer travel direction to an angle less than orequal to the calculated maximum permissible hitch angle; and responsiveto the calculating, outputting a steering control signal to control asteering angle of the vehicle to guide the trailer in the demandedtrailer travel direction.
 9. The method as claimed in claim 8, whereinthe steering control signal is output to an electronic power assistedsteering (EPAS) module to provide automated control of the steeringangle of the vehicle.
 10. The method as claimed in claim 8, furthercomprising determining an actual trailer travel direction based on oneor more sensor signals, and estimating a distance to be travelled by thevehicle at least substantially to match the actual trailer traveldirection with the demanded trailer travel direction.
 11. The method asclaimed in claim 8, further comprising displaying system information fora driver.
 12. The method as claimed in claim 8, further comprisingdisplaying one or more of the following: (a) the actual trailer traveldirection; (b) the demanded trailer travel direction; (c) a numerical orgraphical indication of the estimated distance to be travelled; (d) alocation where the actual trailer travel direction will at leastsubstantially match the demanded trailer travel direction; (e) anangular offset between the actual trailer travel direction and thedemanded trailer travel direction; (f) the maximum permissible hitchangle; (g) a current steering angle; and (h) one or more trajectorylines representing a predicted path of the vehicle and/or the trailer.